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Doc #: 3500-AD-015-0007 Revision: Rev

Azimuth Axis Tuning and Encoder Alignment Procedure

Author(s): Charles Corson

Patrick Dunlop

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Azimuth Axis Tuning And Encoder Alignment Procedure

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1. Contents Revision History .............................................................................................................................. 3

2. Purpose .................................................................................................................................... 4

3. Applicable To ........................................................................................................................... 4

4. Scope ....................................................................................................................................... 4

5. Definitions ................................................................................................................................ 4

6. Training .................................................................................................................................... 4

7. Safety ....................................................................................................................................... 4

8. Personnel, Equipment and Materials Required ...................................................................... 4

9. Notes ........................................................................................................................................ 5

9.1 Critical Comments: ...................................................................................................................5

9.2 Adjusting the Azimuth Axis: .....................................................................................................5

9.2.1 To obtain above plots: ......................................................................................................7

10. Procedure ............................................................................................................................. 5

10.1 On-Sky Verification and Axis Iterations ....................................................................................8

10.2 TPOINT Data Reduction Procedure ..........................................................................................8

10.3 Encoder Alignment ...................................................................................................................9

10.4 Comments: .............................................................................................................................13

11. Procedure Review .............................................................................................................. 14

12. Records .............................................................................................................................. 14

13. References ......................................................................................................................... 14

13.1 Warnings: ...............................................................................................................................14

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Revision History

Rev

Date Approved

Sections Affected

Reason for Change

Remarks and/or Change Details

Name

-- 8-15-2015 Initiated C. Corson

1 4-22-2016 Document Procedure P. Dunlop

Approved by:

SigEng

Name, ME Title

SigEM

Name, EL Maint

SigSci

Name, SciOps

Signature 28 August 2018 Tammie Lavoie, Safety Manager Date

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2. Purpose 1. Aligning and Tuning the Azimuth Axis on the WIYN telescope.

3. Applicable To

4. Scope

1.

5. Definitions 1.

6. Training 1.

7. Safety 2. JHA Form 3. Daily Briefing Form

8. Personnel, Equipment and Materials Required

Tool List Azimuth Tuning/Alignment

Digital Level

Inclinometer JEWEL

Computer Read out Inclinometer

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9. Notes

9.1 Critical Comments:

Tuning of the azimuth encoders is a critical element to the overall procedure. The encoders cannot be ignored at each and every stage along the process. As the azimuth axis is shifted, the encoders are no longer aligned to the disk, in either preload and tip/tilt or yaw/pitch. The digital level is extremely useful in realigning the encoders and may be the only possible aligning tool for pitch/yaw.

An inclinometer will have to be used to align the azimuth axis. The inclinometer is to be “attached” to the azimuth cone plate. This can be done inside the cone. Inside cone, on the far side above of the ladder, locate a bare spot of meal and pre-tapped holes. This plate was configured as a mount for the JEWEL Inclinometer. In the filing cabinets, there is a folder with the ‘data sheet’ that shows how it is hooked up for analog output. (Add to procedure) An accelerometer could potentially be however, it has not been tested in this manner of yet. Accelerometer located in the two grey cabinets on level-b. Has analog output and simple power Input.

The load cells currently in place will provide feedback as to the current preload. The belleville springs/washers are extremely difficult to finely tune and what seems to be tiny adjustments to the preload can have large force changes. One needs to keep 2,500 lbf for a preload, there may be a very narrow azimuth ranges where it dips slightly below this level. Hedge a bit more preload.

10. Procedure

10.1 Adjusting the Azimuth Axis:

The idea behind the inclinometer is, as the azimuth axis turns (computer or manual), the output from the instrument will produce a sinusoidal trace when plotted against azimuth axis or, time if the azimuth is slewed at a constant velocity. As the axis is adjusted such that the axis of rotation is very near vertical, the magnitude of the sinusoid will be minimized. There is a scaling factor for the Jewel Inclinometer and it can be used to provide an angular unit, in sensitivity of an arc second or so (see product data sheet). The graphic below illustrates the point. It will be essential to know which axis aligns with the telescope mount.

Digital level may be used to align the azimuth disk however, the azimuth disk may have too much surface variation for high level of accuracy. The digital level itself is accurate to within 0.01° may be within precision on the order of +/- 5 arcsec. The driving factor is perpendicularity of the disk drive surface and disk top surface and how round the disk drive surface is.

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Figure 1: Sinusoidal output from Jewel, 2-axis inclinometer

1. Mount the Jewell Inclinometer

a. Do Not drop or jar the device, Do Not over-tighten the mount.

b. Ensure that power/signal are secure and wired as per vendor specifications.

2. Rotate the Azimuth Axis to get a data readout from the inclinometer.

3. Adjust the Azimuth axis turnbuckles in pairs, 180° opposing pairs, to keep consistent preload force. See figure below.

a. Avoid adjust only across one diagonal.

b. Fine adjustments to preload forces are allowed.

4. Use the load cell readouts to keep preload force consistent as adjustments made.

5. Rotate Azimuth Axis, the live readout of the inclinometer are used as immediate feedback on adjustments.

6. Iterative process, adjust then rotate to determine if adjustments are in the correct direction.

7. Once the axis is adjusted, the axis of rotation is near vertical, the magnitude of the sinusoid on the inclinometer data readout will be minimized.

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Figure 2: Azimuth Square Frame Restraint Assy, L&F E312005 E. The radial force used to constrain the azimuth axis is applied

theough the preload ajdustment sub assemblies. NE and SE corners, a preload force that is ~2,500 lbf

10.1.1 To obtain above plots:

1. Slew elevation axis to 90d for rough adjustments and lock it there.

2. Slew the azimuth axis to -120°.

3. Slew to 270d. As the axis rotates, record and plot the inclinometers output. If you cannot do this in real time, slow the slew speed to 1 °/sec and hand record the readings every 15 deg.

The gateway laptop contains applications and connects to the data acquisition board setup for these plots. The programs are already setup for recording and displaying all the load cells, indicators, and inclinometers.

1. Initiate software to startup Data Acquisition Module.

a. Control Panel, open layers control panel.

b. Plug in USB devices.

c. Initiate DT9802

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d. Select advanced, acknowledges the board.

e. Ensure all devices are seen.

f. Close.

2. Initiate Measurement Factory software.

a. Open Azimuth Accusation.

3. Begin Tuning Azimuth Axis.

10.2 On-Sky Verification and Axis Iterations

Pointing data will have to be obtained to verify alignment. A 45 pnt map should be adequate, points which cover the entire sky. Doug and Dave will know where to find a grid of Az/El positions.

TPOINT can be used to reduce the data and TPOINT for this job will be easy to use. NOTE: on ivory, WIYN home directory, there is a pointing directory that has some *.tpoint files which is raw data spat out by the tpointlog program, the program that takes out the pointing data from the archive.

The two terms which are imperative to this alignment, AN and AW. These are estimates of the tilt of the axis to the north and west. Positive values indicate a tilt to either N or W but, that’s a vague memory and not certainty.

10.3 TPOINT Data Reduction Procedure

4. Gather the pointing data with the encoder aligned and set to the correct preload (7 lbf). By

making the following alignment adjustments as required ensuring they will perform well.

a. With no preload on the encoder, adjust the entire mount bracket (heavy iron stock) such that the encoder wheel just makes contact with the azimuth axis and the height of the wheel is centered on the azimuth drive disk.

b. Align to precise level (digital level) the encoder block that holds the encoder wheel (pitch & yaw). This is the only mechanical reference. (There is the mount and there is the encoder wheel block which pivots in the encoder mount) This can be easy, it can be difficult, it all depends on various factors.

c. On the WIYN page, ‘m’-page, there is a column for the azimuth axis where the encoder mode can be seen, should be 3.

i. The command to set the modes: ‘az mode #’ where # is 1,2, or 3, encoder 1 or encoder 2 or average both 3. Normal operation is mode 3.

d. The same column will show the encoder counts, based on encoder mode, and the ‘encoder difference’ which is what we are concerned with. After initializing the

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azimuth axis, issue an ‘az encoder reset’ which will set all encoder counters to zero. Re-init that azimuth axis, resets the encoder difference number to something readable and easy to comprehend.

e. As you move the azimuth axis all around, the encoder difference displayed should be small in magnitude compared to the encoder count: 10,000 difference as opposed to 100’s of million counts from the encoders. 100,000 differences and higher have been recorded before. If it is too large in magnitude, the TCS will shut down the axis with the error, “encoder mismatch”. If that is the case, may be able to run for a night on one encoder.

5. OA gathers pointing data making sure to ‘archive enable’ and ‘archive disable’ before/after each pointing data set gathered. (disable archiver, enable archiver, take data set, disable archiver) The last archive file will contain the pointing data.

6. Log into bone and change directories to the archive directory for the month.

a. ssh to bone as wiyn

b. cd to directory ‘archives’ ..it will be up in level from the wiyn home directory.

c. Change to the current month, cd mmmyy

d. Find the archive file named with date stamp and version number. It will be a zipped file if the archiver was properly ‘disabled’. Unzip it, decompress it.

e. Run the command: tpointlog < archive filename > usefulname.tpoint the tpoint extension is needed

f. Export the tpoint file to IVORY into a directory of your choice.

7. Run ‘tpoint' in a xterm. Use the tpoint command ‘indat’ to import the file: indat usefulname.tpoint

8. Load the “default” pointing terms: call altaz or call azalt Update Procedure once Determined

a. This is just a standard set of pointing terms for an alt/az mount.

9. Type the command ‘fit’ to reduce. Results seen immediately and pay attention to AN and AW. If there magnitudes are in the range of 0 - 45, that’s pretty good, 0 - 25 is even better. The units are in arcseconds. As more azimuth terms are added to the model, there are many possibilities, AN and AW may change somewhat but not drastically. Do add tube flexure: ‘use TF’ and fit and azimuth eccentricities: ‘use aces acec’.

10. For a list of commands and more information, type help. A manual is on this disk and Behzad’s webpage.

10.4 Encoder Alignment

A big breakthrough was had in early fall 2015 when Charles Corson used a digital level of ~1 arcmin accuracy (or 6 arcmin) to adjust pitch and yaw of the encoder block. The advantage of this method

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is that it aligns each encoder in a consistent manner. Due to the surface waviness and irregularities of the top drive surface, other methods simply have proven to be inadequate. The result was, the two encoders tracked one another to a high degree (5-10,000 encoder counts out of 100’s of million counts).

In figure 2 below, you see the block being held by the encoder mount. The block is the assembly with the vertical shaft to precisely along to level both in pitch and yaw. Pitch adjustment is somewhat easy though the rotation axis,see the red arrows, are very problematic. If you loosen both clamps too much and there is a preload applied of any kind, the block will be pushed away from the azimuth disk and this is trouble. You want the encoder wheel to protrude so that the encoder mount does not make contact -at all- under any condition or azimuth position with the azimuth drive surface. Yaw and height adjustments are much more problematic and difficult.

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Figure 3: Azimuth Encoder Mount. The encoder instrument is not mounted or shown,. Utilize the top surface of the encoder block for digital level and alignment.

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Figure 4: (Left) Conceptual sketch of Pitch Adjustment and Encoder Wheel Centerline. (Right) Conceptual sketch of Yaw adjustment and Encoder Radial Preload, Black Square is the Pier’s anchor block.

1. Leave the encoder cabled up, plugged in if possible. Otherwise power off the SES so that power is removed from the encoders. Do Not drop them.

2. Remove the encoder and encoder mount being careful not to damage the encoder coupling (metric). This exposes the encoder block as shown in figure 3 above.

3. Remove the preload arm, note: not shown in figure 3. It supplies a radial force at that boss just below the pitch axis noted with the red arrows. During and after the alignment, do not want any preload applied.

4. Carefully loosen the axle clamps keeping some clamping force on them. It’s easy for the block to slip along the axle, creating problems with the encoder wheel engaging the azimuth drive disk correctly.

5. To adjust pitch, find a reliable surface for placing the level on a 1-2-3 block on the encoder block (near the end).

6. Use the micrometer to make pitch adjustments; Note: there is a lot of hysteresis. Applying pressure to the pitch arm so that the micrometer end “touches” the ball underneath is absolutely necessary. For encoder #2, some adjustments, attachments were made to deal with this and the pitch axle shifting so #2 is easier.

7. Adjusting yaw. There are three fine pitched set screws that define the plane for the mount within the pocket that contains the micrometer. This gives “fine” control however, it’s a horrible arrangement.

a. It is determined, one had to be tight with these however, one is making a mistake to use excessive torque, and these are all fine thread.

8. Rough adjustments, particularly for height, are made with the base arm (black bracket that holds the encoder mount in place). Once you start adjusting this, you have to pay very close attention to the centering of the encoder wheel to the azimuth drive disk and to any pitch alignment. It’s tedious but perfectly doable.

9. Install the encoder, ensure the encoder coupling is tightened.

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10. Install the preload arm and spring and make the adjustment necessary to have a 7-8 lbf preload. (Brent, Doug, Mccollum have experience with this)

11. Clean and lubricate azimuth drive disk surface

Note: Encoder 1 is different from Encoder 2. The difference is the flexure plates used. Encoder 1 has very stiff plates and thus, it’s much more critical for it’s encoder wheel to have contact to the azimuth drive disk as the preload spring does not have enough force to overcome the plates. Also, modifications to encoder #2 were made so that the pitch axles could be used more easily and ensure the micrometer kept contact with the ball it reacts against.

10.5 Comments:

The NW ‘stiff’ belleville spring stack (Figure 4 and L&F 312005) may not be behaving as expected, i.e. it maybe mechanically bound, does not return to original state after compression due to ODI mass/moment imbalance (even though it is expected that it have just a few thousandths of a inch compliance). The opposing Belleville stacks are designed to be compliant. Alternatively, spacers should be used to ‘balance’ this static “stiff” spring force though, upon removal of these stacks, no spacers were ever found (E312005). Spacers could be deployed in the NW corner to create a greater static spring force. Having two more load cells to monitor these forces on the static side of the square frame could be used to “balance” the static spring stacks (just because the spring count and arrangement is identical, there would be significant differences in the spring force due to the very high spring constant of the stack and nature of belleville springs).

Figure 5: L&F square spring stacks (corners of square frame). Left (stiff stack) are located on the West side of the frame. Compliant/Adjustment stacks on the East side of frame.

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We assume the azimuth disk is ‘round’. It may not be. The fabrication of the azimuth cone was done on one large lathe as an assembly so it’s believed to be round to 2 ten thousandths of an inch but acceptance measurements estimated this to be more.

The mount is extremely imbalanced from ODI port to HYDRA port and the square frame was simply not designed to accommodate this imbalance (Paragon Engineering and Steve Gunnels who designed the square frame). Aligning the azimuth axis, and final adjustment of the encoders, may best be done with ODI and HYDRA off the telescope.

Calculations to offset the imbalance due to ODI indicated a rather large mass be used to counter ODI’s moment on the azimuth axis. An alternative could be to use an inclinometer as realtime feedback to the TCS and this, available to the pointing data and TPOINT model. This would likely require a two axis inclinometer.

11. Procedure Review 1.

12. Records 1.

13. References KPNO Emergency Manual

13.1 Warnings:

a) Recommend: Examine and study the behavior of the NW drive motor’s coupling to the turnbuckle preload. It may not be providing a proper compliance with changes in AZ disk tilt changes or it may simply be too small a force (Refer to section below).

b) There maybe something unusual with the ball pivot between the turnbuckle and NW motor module. (could the tangent arm on the NW motor be poorly adjusted? Possible orientation of flexure on turnbuckles could be key source to this drive motor decoupling from the drive surface.

c) As you tilt the azimuth axis, the index device (north pier) will change its spacing and it’s entirely possible to destroy this sensor. We have no viable spares. The encoder index switch is a hall-effect switch (SONY MagnaSensor) located on the NORTH location of the pier. Before any adjustments are made, one should make a measurement of this gap so that it can be reset at the end for the day. More importantly, monitor it to ensure one does not tilt the disk such that the magnet and sensor come into contact with one another.

d) As adjustments are made with the azimuth disk, the azimuth encoder will become either ‘no preload’ or ‘excessive preload’ states. The correct azimuth preload is 7-8 lbf. Brent and Doug have knowledge of how this is measured and done. The difficulty here is, it may become an issue where there is no adjustment remaining in the encoder preload bracket and spring (and you do not what this tuned such that the spring is compressed all the way

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or close to it). Two things then have to happen: (a) adjust the entire mount (b) simple decouple the encoder mount entirely and rely on the encoder still in operation.

e) As you tip/tilt the azimuth axis, you will periodically be required to check and adjust the encoder preload and, if required, change the entire alignment of the mount.

f) Do not allow the encoder preload force to exceed ~10 - 12 lbf. This is to protect the encoder wheel.

g) The encoder preload spring must not be left in an adjustment such that the spring is not fully compressed or close to it, must have compliance.

h) Galling is an ever present danger! If a motor starts to slip and spin out of control, stop motion immediately.

It is possible to have a drive motor (SE and NW corners) de-couple from the drive and gall the surface. The drive surface must have lubricant (wipe surface with M3 Starrett Oil for example) but most critical is as the drive disk tilts, the drive motor’s capstan does not tilt to a degree necessary and a zone of high compressive stress in created, galling. The NW motor is most prone to this and all must be very aware of it. It is strongly suspected something is wrong here with the compliance of the motor’s mount to adapt to a change in tilt of the drive surface. This issue should be examined. (Larry Reddell will have knowledge of this pivot.)

Figure 6: Motor Pivot Coupling

draft...10.1.1 to obtain above plots: 1. slew elevation axis to 90d for rough adjustments and lock...

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